TDI based polyurethane foams have been manufactured by the slabstock process for over 50 years. TDI has been the isocyanate of choice for this segment because it produces very low density foams and also a very wide range of foams with the proper selection of formulation components. There is one composition of TDI 8020 (80% 2,4xe2x80x2/20% 2,6xe2x80x2) used for polyether flexible slabstock manufacture and TDI 6535 (65% 2,4xe2x80x2/35% 2,6xe2x80x2) is sometimes blended with TDI 8020 for the manufacture of polyester slabstock. The two attributes that make TDI the material of choice for slabstock are its low density potential and very linear and predictable response in terms of density versus water level.
MDI based polyurethane foams have mainly served the rigid foam, elastomer, and molded flexible foam markets and has not significantly entered into the slabstock flexible market. While MDI flexible foams cannot make the good quality low density and soft foams that TDI is capable, MDI makes excellent medium to higher density both soft and hard foams. There are numerous commercial compositions of MDI for flexible foams, due to the necessity of changing its composition depending on both the formulation components and more importantly the water level. MDI compositions based on high levels of 4,4xe2x80x2 MDI normally lead to foam collapse. It is well known in the art that foam process stability is achieved by increasing the level of 2,4xe2x80x2 MDI and polyfunctional MDI species in the composition. It is also understood that the optimum 2,4xe2x80x2 MDI level and overall MDI functionality is a direct function of the water content of the formulation. A given composition of MDI can only cover a moderate range of water levels, while still giving the desired performance processability (stable yet-open celled foam) and physical properties. Numerous MDI patents illustrate and explain the problems of making stable low density foams from all MDI and also attest to the need for using many compositions. See for example U.S. Pat. Nos. 4,365,025; 5,621,016; 5,089,534; and 5,491,252.
MDI isocyanates have not gained wide acceptance in the TDI slabstock market for two reasons: 1) It would require at least 2 and more likely 3 MDI product compositions to allow for on-the-fly adjustments to the isocyanate composition for varying flexible foam grades. The all-MDI approach would require multiple tank and metering installations for practical slabstock manufacture, making this approach very uneconomical and unwieldy compared to TDI; and 2) The complex non-linear behavior of MDI based flexible foam in regards to its density yield versus water content, makes it very difficult to make predictable adjustments.
MDI/TDI preblends have been widely used with good success in molded application areas and limited success to date in the slabstock area. There is much prior art covering the preparation, processing, and properties of MDI/TDI blends, but none address the issue of a single specific MDI composition blended with TDI to cover all grades and types of flexible polyether polyol based foams. See for example U.S. Pat. Nos. 3,492,251; 5,674,920; 5,132,334; 5,436,277; 5,459,221; 5,491,252; 5,607,982; 5,500,452; 5,232,956; and 4,803,220.
An improved process for the continuous or semi-continuous production of flexible foams, where MDI is the major component and TDI the minor component has now been found. This process substantially obviates the disadvantages described above and allows the use of certain preferred mixtures of diphenyl methane diisocyanates and oligomer polyphenyl-polymethylene polyisocyanates in combination with TDI 8020 or TDI 6535. Good quality, stable yet open celled foam, which does not collapse or shrink, can be achieved over a wide range of densities using a single MDI composition.
The present invention relates to a process for the preparation of flexible polyurethane foam using at least three reactive chemical component streams, wherein the components are fed separately to a mixing device; where at least one component consists essentially of a TDI series isocyanate composition and one component comprises predominantly (i.e., at least 50 weight percent) an MDI series isocyanate component (on a weight basis) and the third component may comprise polyol or another MDI or TDI. It is most preferred that the third component comprises a polyol component.
In an aspect of the invention, the overall isocyanate composition (sum of all isocyanate streams) comprises:
(I) 1 to 40% by weight of toluene dissocyanate and
(II) about 60 to 99% of a mixture of diphenylmethane diisocyanates and polyphenylmethylene polyisocyanates comprising:
(1) 51 to 87% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 0.5 to 16% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 12.5 to 33% by weight of polyphenyl polymethylene polyisocyanates having 3 or more NCO groups per molecule, wherein the sum of (1),(2) and (3) total 100%.
A more preferred polyisocyanate mixture is one in which component (II) comprises:
(1) 59 to 81% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 1 to 13% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates
A most preferred polyisocyanate mixture is one in which component (II) comprises:
(1) 65 to 81% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 1 to 7% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates
In accordance with the invention the 2,4xe2x80x2-MDI content in isocyanate component (II) is low, so that, additional TDI from isocyanate stream (I) is necessary to achieve stable, yet open celled flexible foam. Addition of TDI improves the processing and physical properties of these predominantly MDI based foams compared to the alternative approach of using higher levels of 2,4xe2x80x2 MDI.
An aspect of the invention is the complete control of the MDI/TDI blend ratio by separate metering to a mix device. Preblending or master blending of some of the TDI with the MDI is not the preferred method, but can be done when the MDI composition is extremely low in 2,4xe2x80x2 MDI content, to improve the room temperature liquidity of the MDI composition.
In support of this invention, a new method for the determination of the level of TDI to be used with the particular MDI composition was devised. A guideline empirical calculation allows an overall stability factor to be calculated for any ratio of MDI/TDI. This stability factor for a given formulation is a function of the water level and needs to be increased with increasing water level. This method fulfills the need for making predominantly MDI based flexible polyurethane foams more predictable, like all-TDI based foams. Surprisingly, this empirical model is based on the premise that 2,4xe2x80x2 MDI can be replaced with TDI (both 2,4xe2x80x2 and 2,6xe2x80x2 isomers) on an equivalent molar basis to achieve stable flexible foam.
This invention is directed mainly to flexible foam compositions that contain mainly MDI in the overall isocyanate composition. In this respect, it is a purpose of this invention to modify and improve the performance of predominantly MDI based flexible foams, then to make these hybrid MDI/TDI foams totally equivalent in performance to TDI based foams.
The reactive chemical component streams used for the production of the flexible polyurethane foams according to the invention are described in detail. The overall isocyanate composition comprises at least 2 isocyanate streams (I) and (II) fed separately to a mixing device.
The isocyanate stream (I) can be any commercially available form of toluene diisocyanate (TDI). The most common to the ok slabstock industry is TDI 8020 (80% 2,4xe2x80x2 and 20% 2,6 isomers), but TDI 6535 (65% 2,4xe2x80x2 and 35% 2,6xe2x80x2 isomers) is often blended with the TDI 8020 for polyester slabstock.
The isocyanate stream (II) is a specific mixture of diphenylmethane diisocyanate (MDI) and polyphenylmethane polyisocyanate (PMDI) commonly available. Suitable MDI""s may be pure 4,4xe2x80x2 MDI or mixtures of 4,4xe2x80x2-MDI and 2,4xe2x80x2-MDI isomers. Mixtures of MDI isomers will preferably contain less than 5% by weight of 2,2xe2x80x2-MDI. The PMDI consists of mixtures with diphenylmethane diisocyanate isomers, triisocyanates, and higher oligomers. Such PMDI""s will contain from about 35 to 45% of MDI isomers, 15 to 25% triisocyanates and 35 to 50% by weight of higher oligomers ( greater than 3 functional).
The MDI and PMDI components described above are combined in a manner such that the isocyanate stream (II) comprises:
(1) 51 to 87% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 0.5 to 16% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 12.5 to 33% by weight of polyphenyl polymethylene polyisocyanates of NCO functionality of 3 or greater.
More preferably the isocyanate stream (II) comprises:
(1) 59 to 81% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 1 to 13% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates of NCO functionality of 3 or greater.
Most preferably the isocyanate stream (II) comprises:
(1) 65 to 81% by weight of 4,4xe2x80x2-diphenylmethane dissocyanate
(2) 1 to 7% by weight of 2,4xe2x80x2-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates of NCO functionality of 3 or greater.
The isocyanate stream (II) may optionally be further modified to contain urethane, allophanates, biurets, uretoniimine-carbodiimide, or isocyanaurate linkages. It should be understood that the compositional limitations of stream (II) as explained above do not include any of modified structures, but refer only to the percentage of base MDI structures as described.
The isocyanate stream (II) may be reacted with a polyhydroxy-containing polyol mainly for the purpose of improved liquidity (i.e. resistance to solidification at ambient temperature). Typically, the polyhydroxy-containing polyol will be a polyoxyalkylene polyether polyol, but polyester polyols are also within the scope of this invention. Diol or triols in the range of 500 to 3000 equivalent weight are most preferably used. The isocyanate blend may be reacted to free % NCO""s of greater than 16% to 30%.
It is a most preferred aspect of the invention to maintain the isocyanate components (I) and (II) as separate streams for purposes of complete control of the mix ratio of the TDI(I) and MDI(II) streams. However, when the component (II) contains 7% or less of 2,4xe2x80x2 MDI, then (II) may contain 5 to 10% of blended in TDI for purposes of improved product liquidity. This preblended level of TDI with the MDI must be taken into account, when determining the overall level of TDI in the formulation.
The invention provides a method for determining the proper amount of TDI (I) to be blended with the MDI component (II) in order to make stable, yet open celled flexible foam over a wide range of water levels. Due to the discovery that 2,4xe2x80x2 MDI and TDI 8020 on a molar basis give about the same foam stability, an A empirical formula was derived for the purpose of foam stability prediction. The formula is referred to as the xe2x80x98Isocyanate Asymmetry Factorxe2x80x99 (IAF), since it calculates relative level of the diisocyanate structures (2,4xe2x80x2-MDI, 2,4xe2x80x2-TDI and 2,6xe2x80x2-TDI), which contribute to foam stability by disruption of the 4,4xe2x80x2-MDI polyurea hard block structure:
IAF=((pbw2,4xe2x80x2-MDI/125.2 eq.wt.)+(pbw TDI/87 eq.wt.))xc3x97100/Total NCO equiv. 
Where the Total NCO equivalents is the sum of the free NCO equivalents of all the isocyanate structures in the (I)+(II) isocyanate mixture including 2,4xe2x80x2-MDI, 4,4xe2x80x2-MDI, Poly-oligomeric MDI, 2,4xe2x80x2-TDI and 2,6xe2x80x2-TDI.
IAF can also be described as the Total Equivalents % of 2,4xe2x80x2-MDI plus TDI in the final MDI and TDI mixture.
The IAF values which give stable, yet open celled foam which does not collapse or shrink is a function of the overall formulation composition, polyol type and water level. Flexible foam stability is normally a continuum that operates over some range of composition variables. While the instability, perfect-stability or over-stability of a flexible foam is a function of many compositional variables including the type of polyols used, typical guideline IAF values versus water level are listed below:
Increasing the level of TDI in the overall MDI-TDI composition or the combined (I) and (II) isocyanate streams, increases the IAF value. It has also been discovered that increasing IAF values lead to increased blowing efficiencyxe2x80x94hence lower density foams and also softer foams. Due to the low 2,4xe2x80x2 MDI levels allowed by this invention, the TDI level is of course the major player in foam softening and density reduction. Together the achievement of lower density stable yet open celled foams and also softer foams by this invention provides a novel way of achieving varying grades of foam (i.e. density and hardness) that are required by the slabstock process. The variation of foam grades can be achieved on-the-fly by simple adjustment of the isocyanate stream ratio of (I) to (II).
The invention is primarily directed to the continuous slabstock processes including: maxfoam, conventional pouring, vertifoam, variable pressure foaming, Cardio and other liquid CO2 processing equipment. This invention is not limited to only slabstock and can also be applied to other polyurethane processes. Such processes may be continuous, semi-continuous or batch like reaction injection molding (RIM) of flexible foam, microcellular elastomers, semi-rigid foams and rigid foams. Fully continuous slabstock processes are, however, the most preferred embodiment of this invention.
The separate isocyanate streams (I) and (II) employed in the invention are provided to a mixing device and reacted with a polyol stream (stream III) and any other desirable flexible foam additive streams for producing a flexible polyurethane foam. In one aspect of the invention, as many as 50 streams are utilized. In one embodiment, a polyhydroxy polyol may be used for reacting with the isocyanate streams. Generally, such polyhydroxy polyol has an equivalent weight of about 500 to about 3000 and an ethylene oxide content of less than about 30%. Preferably the equivalent weight is about 1000 to about 2000, more preferably about 1500 to about 2500, and the polyol (or polyol blend) has a functionality of about 2 to about 4, preferably about 2.5 to about 3. Equivalent weight, as is known in the art, is determined from the measured hydroxyl number. Hydroxyl number is the number of milligrams of potassium hydroxide required for complete hydrolysis of the fully acetylated derivative prepared from one gram of polyol.
Polyols which can be utilized in the present invention include both polyether and polyester polyols. Polyether polyols which may be employed include, for example, those based on:
(1) alkylene oxide adducts of polyhydroxyalkanes;
(2) alkylene oxide adducts of nonreducing sugars and sugar derivatives;
(3) alkylene oxide adducts of polyphenols;
(4) alkylene oxide adducts of polyamines and polyhydroxyamines; and
(5) alkylene oxide adducts of phosphorus and polyphosphorus acids.
Suitable poly (alkylene oxide) polyols include those of the HR or high reactivity types and conventional low reactivity types, as so designated by the slabstock industry. Such polyols have an average (nominal) functionality of 2 or greater and an equivalent weight of about 500 to about 2500. More preferably, the poly (alkylene oxide) polyols have an average functionality of about 2 to 3, an equivalent weight of about 1000 to 2500. HR type polyols have greater than about 60% primary hydroxyl functionality, and an ethylene oxide content of less than about 30% by weight. More preferably the HR polyols have greater than about 75% primary hydroxyl functionality and less than about 25% by weight ethylene oxide, and particularly below about 20% by weight ethylene oxide. Conventional slabstock polyols have essentially  greater than 99% secondary hydroxyl functionality. Such polyols comprise about 5% to 15% of ethylene oxide mixed into the polyoxypropylene chain.
Suitable polyols of alkylene oxide adducts of polyhydroxyalkanes include the alkylene oxide adducts of glycerine, 1,2,4-trihydroxybutane, 1,2,6-trihydroxyhexane, 1,1,1-trimethylolethane, 1,1,1-trimethylopropane, pentaerythritol, xylitol, arabitol, sorbitol, mannitol, and the like.
Suitable alkylene oxide adducts of nonreducing sugars and sugar derivatives include sucrose, alkyl glycosides such as methyl glucoside, ethyl glucoside, and the like; glycol glycosides such as ethylene glycol glycoside, propylene glycol glycoside, glycerol glucoside, 1,2,6-hexanetriol glycoside, and the like.
Suitable polyols of alkylene oxide adducts of polyphenols include alkylene oxide adducts of the condensation products of phenol and formaldehyde, adducts of novolac resins and adducts of bisphenols such as bisphenol-A. Also suitable are alkylene oxide adducts of 1,2,3-tris(hydroxyphenyl) propane and of 1,1,2,2-tetrakis(hydroxylphenol)ethanes, and the like.
Other suitable polyols include graft polyols, such as a polyether triol in which vinyl monomers are graft copolymerized. Styrene and acrylonitrile are the usual vinyl monomers of choice. The second type, a polyurea modified polyol, is a polyol containing a polyurea dispersion formed by the reaction of a diamine and TDI. Since TDI is used in excess, some of the TDI may react with both the polyol and the diamine. A third type is a polyisocyanate poly-addition product formed from a dispersion in a base polyol of glycol and amino-polyols reacted with MDI or TDI.
Suitable polyols, which are alkylene oxide adducts of polyamines and polyhydroxyamines include ethylenediamine, propylenediamine, monoethanolamine, diethanolamine, triethanolamine, diisopropanolamine, diethanolmonoisopropanolamine, and the like.
Suitable polyols which are alkylene oxide adducts of phosphorus and polyphosphorus acids include adducts of phosphoric acid, phosphorus acid, alkyl phosphonic acids, and the like.
The most preferred alkylene oxides are propylene oxide and ethylene oxide.
Polyester polyols which may be employed include, for example, those prepared by reacting a polycarboxylic acid or anhydride with a polyhydric alcohol. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may be substituted (e.g., with halogen atoms) and/or unsaturated. Examples of suitable carboxylic acids and anhydrides include succinic acid; adipic acid; suberic acid; azelaic acid; sebacic acid; phthalic acid; isophthalic acid; terephthalic acid; trimellitic acid; phthalic acid anhydride; tetrahydrophthalic acid anhydride; hexahydrophthalic acid anhydride; tetrachlorophthalic acid anhydride; endomethylene tetrahydrophtalic acid anhydride; glutaric acid anhydride; maleic acid; maleic acid anhydride; fumaric acid; and dimeric and trimeric fatty acids, such as those of oleic acid, which may be in admixture with monomeric fatty acids. Simple esters of polycarboxylic acids may also be used, such as terephthalic acid dimethyl ester, terephthalic acid bisglycol ester and mixtures thereof.
Crosslinkers and chain extenders can be included with the polyol. Suitable crosslinkers and chain extending agents include compounds which are reactive with isocyanate groups, particularly compounds which have hydroxyl and/or primary or secondary amine groups including: (1) tri or higher functional crosslinking compounds with an equivalent weight less than about 200 and (2) difunctional chain extender compounds, with an equivalent weight less than about 100. Preferably, the crosslinkers and chain extending agents are predominantly primary hydroxyl terminated.
Suitable cross-linking agents include glycerol, oxyalkylated glycerol, pentaerythritol, sucrose, trimethylolpropane, sorbitol, oxyalkylated polyamines, and alkanolamines. The functionality of the cross-linking agents may range from about 3 to about 8, preferably about 3 to about 4, and the number average molecular weight may vary from about 62 to about 750.
Preferred crosslinking agents include oxypropylated derivatives of glycerol having a number average molecular weight of about 200 to about 750, glycerol and mixtures thereof. Other preferred crosslinking agents include diethanolamine and triethanolamine.
Suitable chain extenders have a number average molecular weight less than about 750, preferably about 62 to about 750, and a functionality of about 2. These chain extenders may be selected from polyols such as ethylene glycol, diethylene glycol, butanediol, dipropylene glycol and tripropylene glycol; aliphatic and aromatic diamines, such as 4,4xe2x80x2-methylene dianilines having a lower alkyl substituent positioned ortho to each N atom; and certain imino-functional compounds such as those disclosed in European Patent Applications Nos. 284 253 and 359 456, and certain enamino-functional compounds such as those disclosed in European Patent Application No. 359 456 having 2 isocyanate-reactive groups per molecule.
The crosslinkers and chain extenders, when used, may be used in an amount of between about 0.1 and 5 parts by weight, preferably between 0.5 and 2 parts by weight per 100 parts of the polyol component.
Surfactants can be included with the polyol component and/or the isocyanate. Silicone surfactants widely used in the polyurethane foam industry, especially those used for conventional (flexible), semi-rigid, rigid, and polyester-based polyurethane foam production, may be employed. Included within the class of such surfactants are organo-polysiloxane polymers and copolymers, the most common ones being the polysiloxane-polyoxyalkylene copolymers wherein the polysiloxane contains greater than about ten silicon atoms. Examples of surfactants which may be employed include TEGOSTAB(copyright) B 4690 from Goldschmidt. Such surfactants may be employed in amounts of about 0.2 percent up to about 1.0 percent by weight, based on the total reaction it mixture.
Catalysts may also be included with the polyol. Useful catalysis include tertiary amine and organometallic polyurethane catalysts. The catalysts are used in amounts necessary for a particular foam as will be evident to one skilled in the art. Typical amounts are from about 0.05 to 1.0 percent based on the combined weight of the A-side (isocyanates) and the B-side (polyol and formulation additives).
Suitable tertiary amine catalysts include: bis(2,2xe2x80x2-dimethylaminoethyl)ether, trimethylamine, N-methylmorpholine, N-ethylmorpholine, N,N-dimethylbenzylamine, N,N-dimethylethanolamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,3-butanediamine, pentamethyldipropylenetriamine, triethylenediamine, pyridine oxide and the like.
Suitable organometallic catalysts include salts of organic acids with metals such as alkali metals, alkaline earth metals, Al, Sn, Pb, Mn, Co, Bi, and Cu, including, for example, sodium acetate, potassium laurate, calcium hexanoate, stannous acetate, stannous octoate, stannous oleate, lead octoate, metallic driers such as manganese and cobalt napthenate, and the like; and organometallic derivatives of tetravalent tin, trivalent and pentavalent As, Sb, and Bi, and metal carbonyls of iron and cobalt. Organotin compounds are preferred metal catalysts. Examples of organotin compounds include dialkyltin salts of carboxylic acids, e.g., dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dilauryltin diacetate, dioctyltin diacetate, dibutyltin-bis(4-methylaminobenzoate), dibuytyltin dilaurylmercaptide, dibutyltin-bis(6-methylaminocaproate), trialkytin hydroxide, dialkytin oxide, dialkyltin dialkoxide, or dialkyltin dichloride, trimethyltin hydroxide, tributyltin hydroxide, trioctyltin hydroxide, dibutyltin oxide, dioctyltin oxide, dilauryltin oxide, dibutyltin-bis(isopropoxide), dibutyltin-bis(2-dimethylaminopentylate), dibutyltin dichloride, dioctyltin dichloride, and the like.
Other known polyurethane catalysts can be used in combination with the amine and organometallic catalysts described above. For example, strong bases such as alkali and alkaline earth metal hydroxides, alkoxides, and phenoxides; acidic metal salts of strong acids such as ferric chloride, stannous chloride, antimony trichloride, bismuth nitrate and chloride, and the like; chelates of various metals such as those which can be obtained from acetylacetone, benzoylacetone, trifluoroacetylacetone, ethyl acetoacetate, salicylaldehyde, cyclopentanone-2-carboxylate, acetylacetoneimine, bis-acetylacetonealkylenediimines, salicyladehydeimine, and the like, with the various metals such as Be, Mg, Zn, Cd, Pb, Ti, Zr, Sn, As, Bi, Cr, Mo, Mn, Fe, Co, Ni, or such ions as MoO2++, UO2++, and the like; alcoholates and phenolates of various metals such as Ti(OR)4, Sn(OR)4, Sn(OR)2, Al(OR)3, and the like, wherein R is an alkyl or aryl, and the reaction products of alcoholates with carboxylic acids, beta-diketones, and 2(N,N-dialkylamino)alkanols, such as the well known chelates of titanium obtained by this or equivalent procedures; all can be employed in the process of the present invention.
Blowing agents may also be included with the polyol component. Suitable blowing agents include reactive blowing agents such as water; and physical blowing agents such as liquefied gases such as nitrogen, carbon dioxide, and air; chlorofluorocarbons and hydrocarbons; chemical blowing agents, such as hydroxyfunctional cyclic ureas, physical polyurethane blowing agents such as methylene chloride, acetone, and pentane. Still other chemical blowing agents include thermally unstable compounds, which liberate gases upon heating such as N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide. Water is the most preferred blowing agent, as it also generates the polyureas making up the hard segments of the flexible foam.
The blowing agents may be used in amounts up to about 15%, preferably about 10 to about 5%, more preferably about 5% to about 0.5% based on the total weight of the B-side. The amount of blowing agent will vary with factors such as the density desired in the foamed product. Water is preferably used as the sole blowing agent in an amount from about 0.5% up to about 8.0% based on the total weight of the B-side.
A variety of additional additives known to those skilled in the art also may be included in the A-side or B-side, preferably the B-side. These additives include flame retardants, colorants, mineral fillers, and other materials.
Suitable additives which may be included in the B-side include, for example, conventional additives such as colorants and flame retardants. Useful flame retardants include organic phosphonates, phosphites and phosphates such as tris-2-chloroisopropyl) phosphate (TCPP), dimethyl methyl phosphonate, and various cyclic phosphates and phosphonate esters known in the art; halogen-containing compounds known in the art such as brominated diphenyl ether and other brominated aromatic compounds; melamine; antimony oxides such as antimony pentoxide and antimony trioxide; zinc compounds such as zinc oxide; aluminum compounds such as alumina trihydrate; and magnesium compounds such as magnesium hydroxide and inorganic phosphorus compounds such as ammonium polyphosphate. The flame retardants may be used in any suitable amount which will be evident to those skilled in the art. For example, the flame retardants may be used in an amount of 0 to 55% based on the total weight of the B-side. Other conventional additives generally used in the art may also be used in the B-side. Examples of these additives include fillers such as calcium carbonate, silica, mica, wollastonite, wood flour, melamine, glass or mineral fibers, glass spheres, etc.; pigments; surfactants; and plasticizers. Such additives can be used in amounts which will be evident to one skilled in the art from the present disclosure.
The invention will now be illustrated by reference to the following non-limiting examples wherein all amounts, unless otherwise specified, are parts by weight.